There is just enough movement in this ice monster’s front feet to offer a sense of menace. Whilst I felt in no immediate danger, and was in full compliance with Yellowstone’s safety guidelines, this was a big bull and his ice coat made him a formidable presence.

There are only so many days in the winter when the morning weather conditions in Yellowstone allow a bull bison to involuntarily morph into a primeval ice monster. The morning must be exceptionally cold (certainly below minus 10º F) to allow the steam rising from the thermal springs and rivers to ice cake all matter nearby, including bison. There are fewer days like this in the National Park than there used to be.

The complication is that the exceptionally cold days tend to be clear, high-pressure days and we must therefore find the bison before the sun takes hold of the light.

In our experience some parts of the road up to Old Faithful from Madison Junction can be shrouded in freezing mist on cold mornings, but there is only a small 60-minute window before that mist and fog evaporate under the sun. In that hour, we must find a bull and settle in under his watchful eye. Our hit rate up here is low and often I have not even taken my camera out of the car.

This is a mythological beast of great presence and power and to be in his company was rather surreal. By 10 am, he was presumably back to being a normal bison, albeit a large one, but by then we had long gone and were warming ourselves up in a frontier town saloon bar and convincing ourselves that we had not just gate crashed a Game of Thrones set.